This invention relates to cellular telephony and, more particularly, to the use of packet techniques in cellular telephony.
The number of people that use cellular telephones is continually increasing. Because the available bandwidth is controlled by governmental regulations, providers of cellular telephony are meeting the increase in users by establishing smaller cell sizes. Smaller cell sizes accommodate larger numbers of mobile units within the same overall bandwidth because smaller cell sizes effectively increase the rate of bandwidth re-use per unit area. However, as cell sizes shrink, mobile units move between cells more frequently. In a circuit switched system, each move requires that one circuit be torn down and another one set up. Consequently, as cell sizes decrease, the work associated with handing off users between cells increases. In addition, when a mobile unit traverses more cells during its connection, it is more likely that the mobile unit will encounter a cell with more units than the bandwidth can support.
Packet switching, as compared to circuit switching, reduces the work required for hand off because addresses embedded within the packets are used to route individual packets rather than setting up and tearing down circuits. Packet switching was used in early military cellular systems. Those networks were designed to be rapidly deployed, were aimed primarily for wireless interconnection between mobile units, and were not connected to a wired backbone network.
Currently, the prevalent commercial cellular system in the United States is a circuit switched arrangement that employs Time Division Multiplexing (TDM). Another system, which is also a circuit switched system, employs Code Division Multiple Access (CDMA). These cellular systems can transmit data in the form of packets, but that does not constitute "packet switching," either in the sense employed in the aforementioned military system or in the sense employed in this disclosure. Specifically, while the data may have a packet format, the switching within the cellular environment is not based on the explicit address information in the packets. For example, in TDM the address is implicit in the frequency and time slot at which the mobile unit operates.
The explicit addressing characteristic of packet switching is more flexible than implicit addressing. With explicit addressing, the capacity on the shared medium can be reassigned as required and the destination can be changed without advance notice. Because of that, it is beneficial to fashion a packet switching approach for cellular communication that interfaces effectively with a wired backbone network.